At the height of its construction, 44,733 people worked on the Panama Canal. The Great Pyramid of Giza required 50,000 workers and the Apollo Project 400,000. No matter what you put on this list, humanity's largest achievements have been accomplished with less than a few hundred thousand workers because it has been impossible to assemble (let alone pay!) more people to work together--until now. With the Internet, we can coordinate the efforts of billions of humans. If 400,000 people put a man on the moon, what can we do with 100 million? My research aims to develop theories and build computer systems that enable massive collaborations between humans and computers for the benefit of humanity. I am working to develop a new area of computer science called human computation, which studies how to harness the combined power of humans and computers to solve problems that would be impossible for either to solve alone.